Syncronizing MFI Throttle Bodies

[Kevin G.]

I'm getting ready to go through the Check / Measure / Adjust procedure, and decided to check the air volume going through the stacks before I dug in. I had not checked it since getting my rebuilt Tbodies back from Eurometrix, since Matt made me promise I wouldn't touch anything except for the idle air screws.

First, I removed the idle air screws and pumped some carb cleaner into the idle air holes. Screws were replaced and set at 2.5 turns from fully closed.

I checked the air flow at 900 rpm, left side came in at 10 on the scale, right side all came in at six. No amount of adjusting on the idle screws would increase the air flow to the right side!

After thinking a bit, I decided to break my promise to Matt and fiddle with the linkage. Since the difference affected the whole bank, I decided to increase the length of the link connecting the cross bar to the right side throttle body to increase the air flow uniformly to the whole side.

One full turn on the cap raised the reading to 7, a second turn made it to 9, and a third raised the right bank to a matching 10. In all, I increased the length of the link by about 2mm.

Now both sides have matching air flow. There is now a hesitation at initial sudden application of throttle (no-load, parked in garage), then it revs freely. Sounds like a mixture issue to me.

Question to the MFI gurus - I haven't gone any farther with the Check Measure Adjust procedure as of yet. Should I heed what Matt Blast said and reset the linkage to it's original setting? I mean, he's the expert and I assume that the setup was done on some kind of flow bench.

Your opinion will be greatly appreciated!

Tomorrow it's compression check, timing recheck and fuel flow check time.

[FA-18C]

Hey Kevin, I "think" that you need to match flow at 3K rpm with the engine at operating temperature. If you balance the stacks at idle, this may have them out of balance at rpm a bit which can cause some popping. If you have the check measure adjust, the 3K is at the top of page 22. disregard is thats how you did it...

[jeff m]

Kevin
I would go back a bit.
Check all your butterflys first to make sure they are all just off the stop. With the links off.(air screws done)
Check the length of the rod from the pump to the rack, that's the important one, it's in the check adjust.
As you return it make sure it does not pull the pump off normal.
As you do every rod, make sure each rod does not pull open a butterfly or move the pump.

The butterflys will give a much bigger adjustment than the air screws. That is why you were not able to "get it done" with the screws.

This is the part I messed up on when I did mine.
By the way number 4 butterfly adj is a *****.

Adjusting the rods can be frustrating, you think youve finished then you find that one butterffy lifts early, check it carefully after you 're done.

But it's really worth it!!!!
Jeff
911T

[jeff m]

Kevin,
Don't worry about the hesitation, that will dissapear as you do your adjustments. I think you effectively leaned it out a bit by increasing the air on one side (when you lengthened a rod)
Jeff
911T

[Kevin G.]

Thanks, all. I appreciate the help.

FA 18C
About 1500 rpm and my syncronizer hits the top of it's scale. I think it was designed for applications with quite a bit less air flow than a 911S. It's the type that looks like a miniature hair dryer. I figure equalizing at a lower rpm is better than not equalizing at all. Do you have a recommendation for a different type of synchro that will work correctly?

PS - can I have a ride in your work vehicle? I promise I will try not to puke!

Jeff M
The whole throttle body package came back to me from rebuild with yellow paint on all the linkage nuts and strict instructions not to mess with anything (except the idle air). I am somewhat reluctant to adjust anything unless there is nothing else left. Before I broke down and sent them in for rebuild, I spent many a frustrating hour trying to get everything to work. You get to the point where everything is looking good, the AARRRRGGGHHH.

You will have to forgive me - I really don't want to have to go through it again unless I have to.

We'll see what tomorrow brings. For some unexplainable reason, I feel something good coming on.

[tmctguer]

for your own sanity, start at the beginning of "Check, Measure and Adjust" and follow the instructions to the letter. it is better than starting in the middle, then wondering why nothing works, THEN starting at the beginning and doing it right...........

[tryan]

if some of your linkage rods are worn out, the rods of older merecedes diesels are much cheaper. the sycro tool should have some air bleeds for higher rpm/flow adjustments. good luck

[jeff m]

Kevin,
I'm sure the guys did an excellent job, but I would still check them all.
Firstlly I would adjust out the adj screw on the micro switch so rack is not held up.
To check them take off one at a time, when replacing it NOTHING
should move, each con rod ball should line up perfectly with the socket before it is pushed on.

At least this way you can move forward knowing that things are good

Jeff

[CamB]

I listened to a discussion this very weekend past between someone who ought to know (been doing it for 20 years) and someone whose engine ran poorly before and well afterwards.

He sychronised them at 2XXX (can't remember, may even have been 3000) revs. You need another synchronometer (or I guess you could try modify yours) if you want to be truely accurate.

[Matt Smith]

Balance them at 2 or 3K plus at idle. They should be the same everywhere. Use a UNISYN, available just about anywhere including here. It will be a little insensitive at idle, but will flow better as the revs increase. It is adjustable.

I would have heeded your rebuilder's advice and not adjusted the rods. He would have set them up perfectly so that each butterfly opens at exactly the same time, and seats the same too. He did this by actually seeing the butterflies and setting their stops correctly. This is why he told you not to touch them.
You have now introduced a new variable into the MFI mix, making getting it right eventually even more of a mystery.

You will find that the adjusting screws often don't do much untill the state of tune approaches close to optimum; then they will work just fine. You need to get everything else around the sytem to be right first. It's totally fundamental to the whole MFI thing.

Think about it: each one of those cylinders should fill at the same rate. Any discrepancies will show through variation in airflow between cylinders. Why are they different? Poss. the valves are set incorrectly, the timing is off or the plug wires etc could be bad, compression fluctuated too much between cylinders?? This is all basic blue book stuff.

Now you have adjusted your cylinders to flow, but you may merely be masking the real cause.
Good luck solving the problem, but I'm guessing it will be hard work now. The air bleed screws were sufficient for the Porsche engineers to get every car they produced in tune before selling it to the public. They should be good enough for you too!!



And yes, the Mercedes connectors are the same, although the rods are steel and not alluminium. They really do weigh quite a bit more. Look for an early MFI merc as well as the diesel models. I'm not sure that I could bring myself to install any ex-diesel part on my Porsche. But ex-MFI? If it was good enough for the Gullwing, it'll be good enough for me (just).

[Kevin G.]

Got to page 16 of C/M/A..

Fuel Injector Pump Timing. Should be a no-brainer. Turned motor to Z1, checked position of rotor. Bingo. One more rotation, past go to FE. Light and mirror in hand, look for the marks to line up.

Huh???

Where's the mark???

OK - Lets try it again. Same results.

Finally I find the mark, almost 90 degrees off. 5 Cogs off overall. I have no idea how this much of a slippage could occur. I still had to fight the belt to get it off then on again.

Any ideas? Has this happened to anyone else??

It would appear that this was the problem, as a short test drive showed that the 3-4K miss was gone. I'll know for sure after a few days of driving. How the car ran at all with the pump out that far is beyond me.

Thanks for all your help!!!!!!!

[Matt Smith]

Excellent news!

That's exactly the sort of thing you have to deal with first!. The Blue book never lies.

I doubt the belt slipped. More likely it wasn't set when the belt was replaced or the pump was moved.

Now all you have to do is reset those push rods and everything will be just fine